Known limits

This page lists what kiro-provider refuses on purpose, what Kiro does not offer, and the open problems it knows of. Everything in the two lists of refusals fails with a typed error that names the field. A few fields are accepted without an effect Kiro can guarantee; the third list names them.

Refused in OpenAI Responses

• background: true, Responses conversation objects, POST /v1/responses/compact and an exact POST /v1/responses/input_tokens (the last two answer 501 unsupported_endpoint).
• Structured Outputs and JSON mode, except one small local profile that Codex CLI uses for thread titles.
• Hosted tools other than web search: File Search, Computer Use and hosted MCP. Kiro has none of them, and kiro-provider does not imitate their events.
• A required, named or constrained tool_choice. auto and none work.
• Remote image URLs and OpenAI file_id references; send images and files inline instead.
• Prompt templates, moderation settings and context management.

Refused in Anthropic Messages

• Context edits that remove content. Only clear_thinking_20251015 with keep: "all" is accepted.
• Structured Outputs, except the same small profile, which Claude Code uses for session titles.
• Forcing a tool, or requiring tools to run one at a time.
• A user message that mixes images of its own with images inside tool results.
• Unknown beta fields and tool versions.

/v1/messages/count_tokens returns an estimate, marked by the response header x-kiro-token-count-mode: estimate. Prompt-cache markers are hints for Kiro, not a guarantee.

What Kiro does not offer

• parallel_tool_calls: false is accepted, but Kiro does not promise to run tools strictly one at a time.
• text.verbosity is accepted as compatibility metadata; Kiro has no verbosity control to pass it to.
• DELETE /v1/responses/{id} removes kiro-provider's local copy. Kiro offers no way to delete its own server-side state for a response, so the gateway cannot promise that.
• store: false turns off the gateway's local copy; it is not a zero data retention promise from AWS.
• Web search runs only with gpt-5.6-sol and claude-opus-5.5 on accounts in us-east-1, the combinations that were tested. Web search

Platforms

• Standalone binaries exist for Linux x64 and ARM64, macOS Intel and Apple Silicon, and Windows x64. There is no Windows ARM64 build.
• The npm package runs on Bun only.

Open problems

• Opus 5 after a finished tool turn. A Claude Opus 5 conversation whose history holds a completed tool turn and a final answer can fail on the next turn with 502 upstream_stream_incomplete. The same request succeeds on Opus 5.5. The cause is upstream and not yet known; kiro-provider does not trim the history to hide it. The audit record has the reproduction.

Each client guide also lists the client versions that were validated; a newer client can send a field that is not supported yet. Protocol compatibility is the complete contract.