[JunyiXu-nv]

Description

/v1/responses reports "parallel_tool_calls": false in the response to every request that does not set the field, while the OpenAI API defaults it to true. The cause is the request model: ResponsesRequest.parallel_tool_calls defaulted to False, and the response echoes the request's value (ResponsesResponse.from_request). The server does not limit how many tool calls a turn has, so the echoed false also misstated what the server did.

This PR changes the default to True, as in the OpenAI API. An explicit null still means "unset" (the request model drops explicitly-null top-level fields), so it reads true as well. A request that sets the field to true or false is unchanged.

API change: this changes the default of a stable API field to match OpenAI. ResponsesRequest.parallel_tool_calls is kind: openai, status: stable in tests/unittest/api_stability/references/trtllm_serve_api.yaml; its default: goes from false to true there, which needs API review. On main nothing but the response echo reads this default, so generation does not change; what changes for clients is the echoed value for requests that omit the field. The release note is added under "TensorRT-LLM Release 1.4" / "API Changes" in docs/source/release-notes.md.

Interaction with #21059: that PR enforces parallel_tool_calls=false on /v1/responses only when the request sets the field explicitly (it checks "parallel_tool_calls" in request.model_fields_set), and a default never appears in model_fields_set. The two changes therefore do not interact and can land in either order. The once-per-process warning that main logs for an explicit false uses the same check and is unaffected.

Not included: enforcing parallel_tool_calls=false (ending generation after the first tool call), which is what #21059 does.

Test Coverage

• tests/unittest/llmapi/apps/test_responses_input_preprocess.py::test_parallel_tool_calls_defaults_to_true_as_in_openai[omitted|null|true|false] (new; the file is cpu_only and already listed in l0_cpu.yml): builds a ResponsesRequest without the field, with null, with true and with false, and checks both the request's value and the value in the JSON of ResponsesResponse.from_request(...): true, true, true, false.
• tests/unittest/api_stability/test_serve_api.py::TestServeAPIStability::test_defaults_match_yaml (existing gate; runs in the A10 stage through unittest/api_stability): checks the updated reference row against the live default.
• tests/unittest/llmapi/apps/test_responses_store_replay.py::test_unenforced_parallel_tool_calls_is_logged_only_when_requested (existing, unchanged): still warns only for an explicit false.

Local runs with a CPU harness that stubs the compiled bindings:

• On main, the new omitted and null cases fail (the request reads false), and with the updated reference row the gate reports [ResponsesRequest.parallel_tool_calls] default drift: code=False vs yaml=True. The true and false cases pass on both. On this branch all pass.
• 11 test files (the seven test_responses_*.py files, test_openai_protocol_parallel_tool_calls.py, test_anthropic_adapter.py, disaggregated/test_disagg_responses_api.py, api_stability/test_serve_api.py): main 456 passed; this branch 460 passed (the 4 new cases); no failures on either.
• Reverting the default to False on this branch fails the omitted and null cases and the gate (3 failures).

PR Checklist

• PR description clearly explains what and why.

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Dev Engineer Review

ResponsesRequest.parallel_tool_calls now defaults to True, consistent with the documented OpenAI API default. An omitted value or explicit null uses True; explicit True and False retain their values. The API reference and release note reflect the change. No current review findings were supplied, so severity counts are unavailable.

QA Engineer Review

The modified preprocessing test covers omitted, null, true, and false inputs and checks the value serialized in the response. The API stability reference test checks the default against the YAML reference. The preprocessing test is listed in tests/integration/test_lists/test-db/l0_cpu.yml. Test results were not independently verified. Coverage verdict: sufficient for the default and explicit-value behavior described.

Per-File QA Perspective

• docs/source/release-notes.md: Verify that the release note accurately describes the /v1/responses default and the behavior of explicit values.
• tensorrt_llm/serve/openai_protocol.py: Verify that omitted and null values resolve to True, while explicit False remains False.
• tests/unittest/api_stability/references/trtllm_serve_api.yaml: The reference default changes to true. Verify that the API stability test matches the live default.
• tests/unittest/llmapi/apps/test_responses_input_preprocess.py: The parameterized test covers all four input cases and checks the serialized response value. It is listed in the CI test list at tests/integration/test_lists/test-db/l0_cpu.yml.

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Walkthrough

The Responses API request default for parallel_tool_calls changes from False to True. Explicit values remain unchanged. Tests, API stability references, and release notes reflect the default and its serialized response value.

Changes

Responses API default

Layer / File(s)	Summary
Request default and behavior validation tensorrt_llm/serve/openai_protocol.py, tests/unittest/llmapi/apps/test_responses_input_preprocess.py, tests/unittest/api_stability/references/trtllm_serve_api.yaml, docs/source/release-notes.md	The request model defaults parallel_tool_calls to True. Tests cover omitted, None, True, and False inputs and check the serialized response value. The API reference and release notes document the updated default.

Priority: Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Possibly related PRs

• NVIDIA/TensorRT-LLM#19883: Adds the Responses API path and logs when parallel_tool_calls=false is accepted but unenforced. This change updates the same request field’s default.
• NVIDIA/TensorRT-LLM#21059: Enforces parallel_tool_calls=false for eligible tool parsers. This change preserves explicit false while changing the default.

Suggested reviewers: qijune, zhaoyangwang-nvidia

Merge Risk: Minimal · up to 51fb1

The release note now describes the changed default and explicit values accurately. No actionable merge risk remains beyond normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Description check		The description follows the template well. It has a Description section that explains the problem, the cause, the fix, and the interaction with #21059. It has a Test Coverage section listing the new a…
Docstring Coverage		No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly identifies the main change: the Responses API now defaults parallel_tool_calls to true. The [None][fix] prefix adds minor noise but does not make the title unclear or unrelated…

Full details: Description check

Explanation

The description follows the template well. It has a Description section that explains the problem, the cause, the fix, and the interaction with #21059. It has a Test Coverage section listing the new and existing tests with local run results. The PR checklist is present, with the first item checked. It also flags the stable API default change for API review, as the template requires for API changes. The description does not name a JIRA, NVBugs, or GitHub ticket, but the title uses [None], so that is acceptable.

Full details: Docstring Coverage

Explanation

No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 2 files. (1 skipped: 1 unsupported.)

Full details: Title check

Explanation

The title clearly identifies the main change: the Responses API now defaults parallel_tool_calls to true. The [None][fix] prefix adds minor noise but does not make the title unclear or unrelated.

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Actionable comments posted: 1

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Inline comments:
Review comments at @docs/source/release-notes.md:
- Line 22: Update the `/v1/responses` release note to clarify that an omitted or
explicitly `null` `parallel_tool_calls` value reports `true`; specify that only
explicit `true` and `false` values retain their requested behavior.

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Reviewing files that changed from the base of the PR and between c9d2dcc and 6f6d52a.

Files selected for processing: 4

• docs/source/release-notes.md
• tensorrt_llm/serve/openai_protocol.py
• tests/unittest/api_stability/references/trtllm_serve_api.yaml
• tests/unittest/llmapi/apps/test_responses_input_preprocess.py

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[JunyiXu-nv]

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