Code written for Claude Sonnet 5 can break on Claude Sonnet 5.5 in five ways

UpdateSep 28, 20265 days agoUnverifiedAdded Oct 2, 2026

Code written for Claude Sonnet 5 can break on Claude Sonnet 5.5 in five ways. To turn off up-front thinking, send thinking: {"type": "between_tools"} instead of "disabled", at high effort or below. Forced tool use (tool_choice types any and tool) returns a 400 error. Thinking blocks are tied to the model and the conversation.

Topics: LLMs, Developer tools

Anthropic's release notes

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Date	Release	Type
Sep 285 days ago	We've launched Claude Sonnet 5.5 (claude-sonnet-5-5) unverified Update	Update
Sep 285 days ago	Thinking blocks that Claude Sonnet 5.5 produces work only in the account that produced them, or in an account unverified Update	Update
Sep 303 days ago	We announced the deprecation of the Claude Sonnet 4.5 model (claude-sonnet-4-5-20250929), with retirement on unverified Deprecation	Deprecation
Sep 258 days ago	Build plugins for Claude unverified Update	Update
Sep 249 days ago	We're expanding which refusals are billed to include refusals that arrive before any output when unverified Update	Update
Sep 249 days ago	We're resuming billing for refusals that arrive before any output when stop_details.category is "bio" unverified Pricing	Pricing
Sep 249 days ago	The Compliance API local session endpoints are out of beta for Claude for Microsoft 365 sessions in Excel unverified Beta	Beta
Sep 249 days ago	The Compliance API Activity Feed no longer returns file names, project document names, or artifact titles unverified Update	Update

Also shipped on Sep 28, 2026

Anthropic in September 2026

Date	Company	Release	Product	Type
Sep 285 days ago	New Relic	Session replay now has its own billing category unverified New RelicPricing	New Relic	Pricing
Sep 285 days ago	Google Cloud	Create custom URLs , like example.cloud.run , that are easy to remember and globally available for your Cloud... unverified Google CloudCloud RunPreview	Cloud Run	Preview
Sep 285 days ago	Google Cloud	To improve security, removed the cloudsql.instances.export permission from the following roles: - Cloud SQL... unverified Google CloudCloud SQLDeprecation	Cloud SQL	Deprecation
Sep 285 days ago	Apple	Xcode 27.2 beta 2 (27B5028f) unverified AppleApple developer releasesBeta	Apple developer releases	Beta
Sep 285 days ago	Netlify	Prompt and preview in one view with Agent Runners unverified NetlifyPreview	Netlify	Preview
Sep 285 days ago	Cloudflare	Workers, Cloudflare CLI - Cloudflare CLI is now in beta unverified CloudflareCloudflare developer platformBeta	Cloudflare developer platform	Beta

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Also shipped on Sep 28, 2026

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