Parameters - Phaseo Docs

This page is the field-by-field reference for request parameters exposed by Phaseo. Use it when you want to know:

what a parameter does
what type it expects
the typical range or accepted values
whether it changes quality, cost, latency, or routing behavior

If you want tuning advice instead of field definitions, use Inference Parameters and Sampling and Decoding. Parameter support still varies by endpoint, model, and provider. The model quickstart table shows support aggregated across currently active providers for a specific route.

Quick lookup

Parameter	Type	Use it for
`model`	`string`	Selecting the gateway model id to run.
`stream`	`boolean`	Returning SSE output incrementally instead of one final payload.
`temperature`	`number`	Increasing or reducing randomness.
`top_p`	`number`	Narrowing or widening the nucleus sampling pool.
`top_k`	`integer`	Restricting sampling to the top-k candidate tokens.
`max_tokens`	`integer`	Capping output length on routes that still use this field name.
`max_output_tokens`	`integer`	Capping output length on routes that use the newer field name.
`max_completion_tokens`	`integer`	Capping output length on newer OpenAI-style text APIs.
`frequency_penalty`	`number`	Discouraging repeated tokens and phrases.
`presence_penalty`	`number`	Encouraging topic or vocabulary change.
`repetition_penalty`	`number`	Provider-specific anti-repetition control.
`seed`	`integer`	Improving reproducibility when the upstream provider supports it.
`stop`	`string` or `string[]`	Defining explicit stop sequences.
`logprobs` / `top_logprobs`	`boolean` / `integer`	Requesting token probability data.
`tools`, `tool_choice`	`array`, `string`, `object`	Tool calling and function execution control.
`parallel_tool_calls`	`boolean`	Allowing or forcing sequential tool execution behavior.
`response_format`	`string` or `object`	Plain text, JSON, or schema-constrained output.
`json_schema`	`object`	Defining the schema for structured output workflows.
`structured_outputs`	`boolean`	Capability signal for reliable schema-constrained output.
`reasoning`	`object`	Provider-specific reasoning configuration.
`reasoning_effort`	`string`	Lowering or increasing reasoning budget.
`reasoning_tokens`	`integer`	Reasoning-specific token limit or accounting field.
`include_reasoning`	`boolean`	Returning reasoning content or summaries where supported.
`service_tier`	`string`	Choosing a supported request tier such as `priority` or `flex`; OpenAI also accepts `fast` as an alias.
`prompt_cache_key`	`string`	Keeping cache-aware routing sticky for related requests.
`cache_control`	`object`	Applying provider-neutral prompt cache hints or breakpoints.
`prompt_cache_retention`	`string`	Setting OpenAI-compatible prompt cache retention.
`provider`	`object`	Influencing routing and provider selection.
`provider_options`	`object`	Passing provider-native settings through the gateway.
`meta` / `usage`	`boolean`	Returning extra metadata or usage accounting in the response.
`debug`	`object`	Requesting routing traces and diagnostic payloads.

Endpoint notes

service_tier is supported on the main text request surfaces:

Use priority or flex only when the selected model and provider combination supports them. Phaseo keeps priority as the canonical premium tier; OpenAI routes also accept fast as an alias. standard is the default when service_tier is omitted. Batch is not a service_tier value. Batch requests use the separate Batch API. For Anthropic-compatible Messages requests, Anthropic’s native upstream values are auto and standard_only. Phaseo may normalize or map these values across providers while preserving Anthropic-compatible behavior on /v1/messages. If you are using an official Anthropic SDK with a custom base URL pointed at Phaseo, prefer Anthropic-native values on /v1/messages. For normalized cross-provider tier controls such as priority and flex, or OpenAI’s fast alias, prefer raw HTTP requests or the gateway-native / OpenAI-style text APIs.

Parameter reference

`model`

Selects the gateway model id for the request.

Field	Value
Type	`string`
Required	Yes
Example	`openai/gpt-5-nano`

Use the canonical model id shown on each model page quickstart unless you intentionally want to rely on an accepted alias. Canonical ids are the safest choice for examples, automation, and long-lived integrations.

`stream`

Returns output incrementally over Server-Sent Events instead of waiting for one final response body.

Field	Value
Type	`boolean`
Default	`false`
Typical values	`true`, `false`

Turn this on for chat UIs, token-by-token rendering, or long responses where early output improves UX. Leave it off when you want one complete JSON response, simpler retries, or easier structured parsing. Notes:

Streaming support varies by endpoint.
Streaming is usually a transport choice, not a quality control.
Tool-calling or structured-output flows may still stream differently by provider.

`temperature`

Controls how random token selection can be.

Field	Value
Type	`number`
Typical range	`0.0` to `2.0` when supported
Default	Provider and model specific
Good starting point	`0.2` to `0.7`

Lower values make output more conservative and repeatable. Higher values increase variety, which can help for brainstorming or creative writing but can also reduce consistency and schema adherence. Good fits:

extraction
classification
JSON or schema output
creative generation

Practical guidance:

Start low for structured tasks.
Change either temperature or top_p first, not both.
High temperature plus aggressive quantization can magnify instability.

`top_p`

Applies nucleus sampling by limiting candidates to the smallest token set whose cumulative probability mass reaches top_p.

Field	Value
Type	`number`
Typical range	`0.0` to `1.0` when supported
Default	Provider and model specific
Good starting point	`0.9` to `1.0`

Lower values make the model choose from a narrower probability mass, which usually produces safer and more focused output. Higher values let the model consider a broader set of tokens. Notes:

Tune top_p when you want a narrower or broader search space without directly changing temperature.
For most applications, moderate temperature and near-1.0 top_p is a reasonable baseline.

`top_k`

Restricts sampling to the top-k candidate tokens at each step on providers that expose it.

Field	Value
Type	`integer`
Typical range	`>= 1` when supported
Default	Provider and model specific

Lower top_k values tighten the model’s choices and can make output more predictable. Higher values widen the candidate pool. Notes:

top_k is not available on every provider.
Treat it as a more explicit token-pool limiter than top_p.

`max_tokens`

Caps output length on endpoints and providers that still use the max_tokens field name.

Field	Value
Type	`integer`
Typical range	`>= 1`
Default	Provider and model specific

Use it to control cost, latency, and truncation risk. If this value is too small, the output can appear incomplete even when the model behaved correctly.

`max_output_tokens`

Caps output length on routes that use max_output_tokens instead of max_tokens.

Field	Value
Type	`integer`
Typical range	`>= 1`
Default	Provider and model specific

This is semantically the same kind of control as max_tokens, but you should send the field name expected by the selected endpoint or SDK surface.

`max_completion_tokens`

Caps output length on newer OpenAI-style text APIs that use max_completion_tokens.

Field	Value
Type	`integer`
Typical range	`>= 1`
Default	Provider and model specific

This is another output-token budget field. Use the endpoint’s expected name rather than mixing output-length aliases in one request shape.

`frequency_penalty`

Discourages repeated tokens in proportion to how often they have already appeared.

Field	Value
Type	`number`
Typical range	Commonly `-2.0` to `2.0` when supported
Default	Usually `0`

Raise this when the model loops, repeats phrases, or overuses the same wording.

`presence_penalty`

Discourages reusing tokens once they have appeared at all, which can help the model explore new topics or wording.

Field	Value
Type	`number`
Typical range	Commonly `-2.0` to `2.0` when supported
Default	Usually `0`

Compared with frequency_penalty, this is usually a broader novelty control rather than a repeat-count control.

`repetition_penalty`

Applies provider-specific anti-repetition behavior outside the classic OpenAI-style penalty fields.

Field	Value
Type	`number`
Typical range	Provider and model specific, often around `0.0` to `2.0`
Default	Provider and model specific

The intent is similar to frequency_penalty and presence_penalty, but the semantics vary more by provider. Treat it as provider-native behavior rather than a universally identical control.

`seed`

Requests deterministic sampling when the upstream provider supports seeded generation.

Field	Value
Type	`integer`
Default	Unset

Use this for debugging, regression testing, and reproducing behavior as closely as the upstream platform allows. Seeded generation improves reproducibility, but exact determinism is not guaranteed across all providers or infrastructure changes.

`stop`

Defines one or more sequences that terminate generation early.

Field	Value
Type	`string` or `string[]`
Default	Unset
Common use	Parser boundaries, template endings, protocol markers

This is useful when you need hard output boundaries, such as stopping before a footer, tool delimiter, or next synthetic section.

`logprobs`

Requests token-level probability metadata where available.

Field	Value
Type	`boolean`
Default	`false`

This is mainly useful for analysis, evaluation, ranking, debugging, and confidence-style workflows. It is not usually needed for standard product responses.

`top_logprobs`

Requests the top alternative candidate tokens for each output position alongside their log probabilities.

Field	Value
Type	`integer`
Typical range	Provider specific, often `0` to `20`
Requires	`logprobs: true`

Use this when you need to inspect alternative token branches rather than only the chosen output token.

`tools`

Declares callable tools or functions for tool-using model workflows.

Field	Value
Type	`array`
Default	Unset

Use the OpenAI-style tool schema unless the endpoint docs say otherwise. Tool declarations describe what the model may call, not whether it must call one.

`tool_choice`

Controls whether the model may call tools automatically, must not call tools, or must use a specific tool.

Field	Value
Type	`string` or `object`
Common values	`none`, `auto`, `required`

Use none when you want content only, auto when the model may decide, and stricter values when downstream orchestration requires a tool call.

`parallel_tool_calls`

Allows or disallows concurrent tool calls on compatible tool-calling APIs.

Field	Value
Type	`boolean`
Default	Endpoint and provider specific

Disable this when downstream systems require strictly sequential execution, ordered side effects, or simpler agent traces.

`response_format`

Requests a particular output format such as plain text, JSON, or schema-constrained responses.

Field	Value
Type	`string` or `object`
Default	Endpoint and provider specific

Exact accepted shapes depend on the endpoint and provider adapter. Use this when you want more than free-form text, especially for JSON responses and structured extraction flows.

`structured_outputs`

Signals support for reliably structured or schema-constrained responses on the selected route and provider set.

Field	Value
Type	`boolean`
Meaning	Capability signal rather than a direct tuning knob

In quickstart tables, this helps you understand whether the selected endpoint and active providers can reliably support structured-output workflows. It is best interpreted as support metadata.

`json_schema`

Supplies the JSON schema used for structured output enforcement on compatible models and endpoints.

Field	Value
Type	`object`
Used with	Structured output or schema-constrained response flows

Use this when your application needs guaranteed fields, typed extraction, or a strict response contract. Keep schemas narrow and task-specific for better adherence.

`reasoning`

Contains provider-specific reasoning configuration for reasoning-capable APIs.

Field	Value
Type	`object`
Default	Unset

Depending on the route, this may include enablement, effort, token budget, verbosity, or whether reasoning content is returned.

`reasoning_effort`

Requests a lower or higher reasoning budget when the endpoint and model expose that control.

Field	Value
Type	`string`
Common values	Provider specific, often values like `minimal`, `low`, `medium`, `high`, `none`
Default	Provider and model specific

Higher effort can improve difficult reasoning tasks at the cost of latency and token usage. Lower effort is often a better fit for faster, cheaper requests.

`reasoning_tokens`

Represents a reasoning-specific token field where supported.

Field	Value
Type	`integer`
Default	Provider and model specific

Depending on the route, this may be a request knob, a limit, or a response accounting field rather than a universally supported request parameter.

`include_reasoning`

Requests reasoning content or reasoning summaries in responses where supported.

Field	Value
Type	`boolean`
Default	`false`

Use this carefully. Reasoning payloads can be larger, may not be available on every model, and may be a poor fit for production responses that do not need extra diagnostic detail.

`service_tier`

Selects a supported routing or pricing tier on compatible text APIs.

Field	Value
Type	`string`
Supported values	`standard`, `fast`, `priority`, `flex`
Default	`standard`

Use priority or flex only when the chosen model and provider combination supports them. Phaseo keeps priority as the canonical premium tier; supported OpenAI routes also accept fast as an alias with identical routing and pricing. Omit the field to stay on the default standard tier. Phaseo maps these gateway-normalized tier values to provider-native controls internally, so callers can use the same service_tier values across supported text surfaces. Notes:

Batch is a separate API flow, not a service-tier value.
Support varies by endpoint and provider.

`prompt_cache_key`

Provides a stable cache affinity key for prompt-cache-aware routing.

Field	Value
Type	`string`
Use for	Sticky routing for related cached prompts

Use this when a series of requests share stable prompt prefixes and should prefer the same upstream provider or region when possible. Phaseo can also derive cache affinity from request context, but an explicit key is better for long-running conversations, agent sessions, and repeated workflows.

`cache_control`

Applies a provider-neutral prompt cache policy on supported text request surfaces.

Field	Value
Type	`object`
Common fields	`type`, `ttl`, `scope`
Use for	Automatic prompt caching and explicit cache breakpoints

Use top-level cache_control on Chat Completions, Responses, and Anthropic Messages requests when you want the same cache hint to travel through the gateway’s common schema. You can also place cache_control on supported content blocks when you need explicit cache breakpoints. Typical TTL values are 5m and 1h, depending on provider and model support. Provider-specific aliases such as provider_options.anthropic.cache_control and provider_options.google.cache_control remain accepted for native integrations.

`prompt_cache_retention`

Sets the OpenAI-compatible prompt cache retention policy on supported OpenAI-routed requests.

Field	Value
Type	`string`
Example	`24h`
Use for	OpenAI prompt cache retention

Use this when you want to pass OpenAI cache-retention options without nesting them under provider-specific options. The provider-specific alias provider_options.openai.prompt_cache_retention remains accepted. When both are present, the top-level prompt_cache_retention value takes precedence.

`provider`

Contains routing constraints and provider preferences.

Field	Value
Type	`object`
Use for	Routing rules, provider selection, compliance constraints

Use this when you want to influence which upstream providers may execute the request, how they should be ranked, or what compliance requirements must be satisfied. Common fields include:

Field	Type	Purpose
`order`	`string[]`	Preferred provider order.
`only`	`string[]`	Restrict routing to specific providers.
`ignore`	`string[]`	Exclude specific providers.
`include_alpha`	`boolean`	Allow alpha providers in routing decisions.
`sort`	`string` or `object`	Rank providers, often by `price`, `latency`, or `throughput`.
`required_execution_region`	`string`	Restrict execution to a required region.
`required_data_region`	`string`	Restrict data handling to a required region.
`require_zero_data_retention`	`boolean`	Require providers that meet zero-data-retention constraints.
`max_price`	`object`	Set ceilings for prompt, completion, image, audio, or request costs.
`quantizations`	`string[]`	Narrow routing to specific quantization variants when supported.

`provider_options`

Contains provider-specific passthrough settings that should not be normalized into the shared gateway request shape.

Field	Value
Type	`object`
Use for	Provider-native controls

Examples include:

openai.context_management
openai.prompt_cache_retention
anthropic.cache_control
google.cache_control
google.cached_content

Use this when you need a provider-native feature but still want the rest of the request to stay on the gateway’s common schema. Prefer top-level cache_control for common cache hints and top-level prompt_cache_retention for OpenAI-compatible retention. For provider prompt caching examples across Chat Completions, Responses, and Anthropic Messages, see Prompt Caching.

`meta`

Requests extra response metadata where supported.

Field	Value
Type	`boolean`
Default	Endpoint specific

Use this when you want additional non-core response metadata for debugging, analytics, or downstream inspection.

`usage`

Requests usage accounting details where supported.

Field	Value
Type	`boolean`
Default	Endpoint specific

This is useful when you want explicit token or usage accounting in the response body rather than only relying on headers or dashboards.

`debug`

Enables controlled request and routing diagnostics.

Field	Value
Type	`object`
Use for	Development and troubleshooting only

Supported debug fields include:

Field	Type	Purpose
`enabled`	`boolean`	Enable debug mode for the request.
`return_upstream_request`	`boolean`	Include the transformed upstream request payload.
`return_upstream_response`	`boolean`	Include upstream response payload where available.
`trace`	`boolean`	Return routing or debug traces.
`trace_level`	`summary` or `full`	Control trace verbosity.

Debug payloads can contain sensitive request context. Use them only in development or tightly controlled environments.

Example request

{
  "model": "openai/gpt-5-nano",
  "input": "Summarize this changelog.",
  "stream": false,
  "temperature": 0.3,
  "max_output_tokens": 300,
  "provider": {
    "order": ["openai", "anthropic"],
    "ignore": ["some-provider"],
    "sort": "latency",
    "required_execution_region": "eu",
    "require_zero_data_retention": true
  },
  "debug": {
    "enabled": true,
    "trace": true,
    "trace_level": "summary"
  }
}

Detailed explanations

If you want the deeper “how should I tune this?” guidance rather than the raw field reference, use these next:

Inference Parameters for practical advice on temperature, top_p, top_k, max token limits, stop sequences, and tuning workflow
Sampling and Decoding for how randomness, penalties, and decoding controls change model behavior

​Quick lookup

​Endpoint notes

​Parameter reference

​model

​stream

​temperature

​top_p

​top_k

​max_tokens

​max_output_tokens

​max_completion_tokens

​frequency_penalty

​presence_penalty

​repetition_penalty

​seed

​stop

​logprobs

​top_logprobs

​tools

​tool_choice

​parallel_tool_calls

​response_format

​structured_outputs

​json_schema

​reasoning

​reasoning_effort

​reasoning_tokens

​include_reasoning

​service_tier

​prompt_cache_key

​cache_control

​prompt_cache_retention

​provider

​provider_options

​meta

​usage

​debug

​Example request

​Detailed explanations

​Related pages