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Anthropic SDK Releases — August–September 2026 (Python v1.1–v1.9, TypeScript sdk-v0.121–v0.129 + Bedrock/Vertex/Foundry)

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Source: raw/anthropic-watch-anthropic-sdk-python-tag-v1-{1..9}-0.md and raw/anthropic-watch-anthropic-sdk-typescript-tag-{sdk-v0-121-0,sdk-v0-128-0,sdk-v0-129-0,bedrock-sdk-v0-33-2,bedrock-sdk-v0-34-0,vertex-sdk-v0-20-0,foundry-sdk-v0-5-0}.md (Stainless-generated GitHub releases, 2026-08-26 → 2026-09-28), plus the anthropics/skills commits 53048666, 34040c9c, 33375500 and 8a1541c4 that document the same API surface in the claude-api skill, and cookbook commit 6b671ef6 (Admin API notebook).

Project: anthropics/anthropic-sdk-python, anthropics/anthropic-sdk-typescript · URL: https://github.com/anthropics/anthropic-sdk-python/releases · Version: Python v1.1.0 → v1.9.0; TypeScript sdk-v0.121.0 → sdk-v0.129.0

The Python SDK shipped nine minor releases in the five weeks after its breaking 1.0.0 (2026-08-20, covered in the May–July SDK article), and the TypeScript SDK stayed on 0.x. Two model IDs landed: claude-opus-5-5 (Python v1.8.0 / TS sdk-v0.128.0, 2026-09-22) and claude-sonnet-5-5 (Python v1.9.0 / TS sdk-v0.129.0 and the Bedrock, Vertex and Foundry packages, 2026-09-28). The other headlines are cache diagnostics going GA, auto-mode tool permissions for Managed Agents, Organization API endpoints, a compaction beta, and a tool runner that can start tool calls while the reply is still streaming.

Key Takeaways

  • Bump to Python v1.8.0 / TS sdk-v0.128.0 for Opus 5.5, and v1.9.0 / sdk-v0.129.0 for Sonnet 5.5. For Sonnet 5.5 on the cloud providers, the TypeScript packages are bedrock-sdk-v0.34.0, vertex-sdk-v0.20.0 and foundry-sdk-v0.5.0. See Claude Opus 5.5 and Claude Sonnet 5.5.
  • Cache diagnostics are GA (Python v1.9.0 / TS sdk-v0.129.0): a diagnostics field on Message and MessageCreateParams. The beta dates to Python v0.102.0 / TS sdk-v0.96.0 in May. The claude-api skill’s cost-optimize flow now points cache misses at it (skills 8a1541c4). See Prompt Caching for Agencies.
  • Three breaking or tightening changes in minor releases — check these before upgrading:
    • webhooks.unwrap() requires headers (Python v1.2.0).
    • Beta user profiles removed relationship in favour of access_type (Python v1.3.0).
    • Credentials files readable by group or others are refused (Python v1.5.0).
  • Managed Agents got an auto permission policy (Python v1.5.0, repeated in v1.6.0). The claude-api skill describes it as a third option beside always_allow / always_ask: the action runs, is denied as high-risk with an error tool result while the session keeps running, or pauses for approval when indeterminate — and warns it is “not a human checkpoint” (skills 34040c9c). See Managed Agents.
  • The tool runner grew up across the period. It keeps going on pause_turn (v1.1.0), gained compact_before_next_turn() (v1.7.0), made add_tools() / addTools() take effect straight away (v1.8.0 / sdk-v0.128.0), and can optionally run tool calls while the reply streams (v1.9.0 / sdk-v0.129.0).
  • Files and Skills APIs moved to GA shapes. Python v1.2.0’s beta files/skills namespaces use GA shapes and drop dated beta header pins; the claude-api skill says both APIs “are out of beta” and its examples call client.files.* / client.skills.* with no beta header (skills 53048666).
  • TypeScript deprecated the betas param on GA models and completions methods, and removed client-side compaction control from its tools (sdk-v0.129.0, both filed as chores).

Python v1.1.0 → v1.9.0

VersionDateHighlights
v1.1.02026-08-26”updates” thinking display mode (beta); Organization API endpoints; tool runner keeps going on pause_turn; legacy response API removed (filed as an internal chore)
v1.2.02026-08-27Beta files/skills namespaces use GA shapes and drop dated beta header pins; webhooks.unwrap() requires headers; AWS/Bedrock sign raw request bytes so binary uploads work; agent toolset and memory tool preserve exact file bytes
v1.3.02026-09-01Beta user profiles: external_user_onboarded_at added, relationship removed in favour of access_type; organization compliance settings; batch results on GA raw/streaming response wrappers; an unexplained “api: manual updates” entry
v1.4.02026-09-04Claude Tag category and user breakdowns in usage reports; workspace ID on more endpoints; clear error when an httpx object is passed instead of httpx2
v1.5.02026-09-10Auto mode tool permissions for Managed Agents; content_too_large web_fetch error; public GitHub repos mount without authorization_token in Managed Agents sessions; Message.to_param(); tool objects accepted directly in messages.create/parse/stream/count_tokens; credentials files readable by group/others refused; idempotency_key kept as a deprecated no-op
v1.6.02026-09-15compaction parameter and signed compaction blocks (beta); thinking_mismatch_allowed in input_transformations (beta); url_sources on web fetch; async credential token providers; honours Retry-After above 60 seconds; async client retries connection errors
v1.7.02026-09-18Rate limits gain group with display_name, group_type deprecated; tool runner compact_before_next_turn(); Bedrock raises an API error for eventstream exception frames; multiple anthropic-beta values joined with a comma and no space; requires pydantic 1.10+
v1.8.02026-09-22claude-opus-5-5; inline tool definitions and MCP tool-list pinning (beta); one shared evaluated_permission enum across Managed Agents events; Dreams API reference docs
v1.9.02026-09-28claude-sonnet-5-5; between_tools thinking type (degrades to disabled on fallback hops); cache diagnostics GA; tool runner can run tool calls while the reply streams; workspace rate limits include_inherited and source; typed event-type filter for Managed Agents events; parse and tool runner stop sending the beta header

The Organization API endpoints in v1.1.0 are the client.beta.organization surface that the cookbook’s new Admin API notebook (2026-09-18) exercises: invites and roles, workspaces and members, an API key audit, service accounts and rate limits (cookbook 6b671ef6). See Claude Cookbooks.

TypeScript

  • sdk-v0.121.0 (2026-08-26) — the same feature set as Python v1.1.0 (updates thinking display beta, Organization API endpoints, tool runner on pause_turn), plus Standard Schema support for structured outputs and tools. Examples switched to adaptive thinking.
  • sdk-v0.128.0 (2026-09-22) — claude-opus-5-5, inline tool definitions and MCP tool-list pinning (beta); addTools() takes effect straight away; the tool runner’s compaction request leaves out reply-only params.
  • sdk-v0.129.0 (2026-09-28) — claude-sonnet-5-5, between_tools thinking, a ClientToolUnion type for client-executed tools, cache diagnostics GA, optionally start tool calls while the reply streams, and a partial-JSON streaming fix that shows every complete array item and holds back unfinished numbers. Chores: deprecate the betas param on GA models and completions methods, and remove client-side compaction control from tools.
  • bedrock-sdk-v0.33.2 (2026-08-26) — never sends ambient first-party credentials to the Mantle endpoint.
  • bedrock-sdk-v0.34.0, vertex-sdk-v0.20.0, foundry-sdk-v0.5.0 (2026-09-28) — each adds claude-sonnet-5-5.

The claude-api skill as release notes

The anthropics/skills commits document API behaviour the SDK changelogs only name:

  • Fable 5.1 / Mythos 5.1 (skills 53048666, 2026-09-01): claude-fable-5-1 and claude-mythos-5-1 become the default Fable-tier IDs; per-message effort (mid-conversation-output-config beta); turn-scoped mid-conversation system messages with clear_at; thinking.display "updates" for progress between tool calls (apparently the “updates” display mode the SDKs added in v1.1.0 / sdk-v0.121.0^[inferred]); thinking block_binding controls; a 0.025x cache-read rate on Fable 5.1 with a max_tokens: 0 keep-alive. See Claude Fable 5.1 + Mythos 5.1.
  • Managed Agents auto policy (skills 34040c9c, 2026-09-10): the evaluated_permission and evaluation fields on agent.tool_use / agent.mcp_tool_use; client code should gate on evaluated_permission === 'ask' rather than the configured policy; ant beta:sessions connect terminal viewer; the deny field is deny_message, not message.
  • Refusal billing (skills 33375500, 2026-09-24): a refusal before any output counts against rate limits; a mid-stream refusal bills input tokens plus the output already streamed.
  • Opus 5.5 / Sonnet 5.5 (skills 8a1541c4, 2026-09-29): Opus 5.5 is the skill’s default model and Sonnet 5.5 the current Sonnet; streaming client tools default to eager_input_streaming; model access failures are a 404 and beta gating a 400, not a 403; ant apply is recommended for version-controlled Managed Agents resources.

Try It

  • Pin anthropic>=1.9.0 (Python) or @anthropic-ai/sdk@0.129.0 (TypeScript) to get both new model IDs and cache diagnostics GA.
  • Before upgrading Python past v1.2.0, grep for webhooks.unwrap( and pass the request headers.
  • Before upgrading past v1.5.0, check that your credentials file is not readable by group or others (chmod 600).
  • Read diagnostics on responses to find out why a prompt-cache read missed, instead of inferring it from usage.
  • If you run Managed Agents unattended, evaluate the auto policy — and treat it as a classifier, not a reviewer.

Open Questions

  • Did a claude-fable-5-1 model constant land in any SDK? No SDK release in this batch names it. Python v1.3.0 (2026-09-01, the Fable 5.1 launch day) carries an unexplained “api: manual updates” entry.
  • TypeScript sdk-v0.122.0 through sdk-v0.127.0 are not in these sources (sdk-v0.128.0 diffs against v0.127.0), nor are bedrock-sdk v0.33.3–v0.33.8 (v0.34.0 diffs against v0.33.8).
  • What are “inline tool definitions” and “MCP tool-list pinning”? Both are one-line beta entries in v1.8.0 / sdk-v0.128.0 with no documentation link.
  • What does between_tools thinking do? The changelogs add the type and say it degrades to disabled on fallback hops; its behaviour is not described.
  • Will TypeScript follow Python to 1.0? Still no announcement.

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