One post tagged with "bedrock"

Date: July 4 to July 10, 2026
Affected versions: v1.91.0 and v1.91.1
Severity: Medium (silent cost regression; no correctness impact)
Status: Resolved in v1.91.2

Note: If you run Claude Code against Amazon Bedrock through LiteLLM on either v1.91.0 or v1.91.1, upgrade to v1.91.2 or higher.

Summary​

Between July 4 and July 10, proxies running v1.91.0 or v1.91.1 silently broke Anthropic prompt caching for Claude Code sessions routed through Amazon Bedrock's Invoke API. For the customers who reported it, warm-session cache hit rates dropped from roughly 90% to 25-45% and team daily spend rose 2-3x for the same usage. Requests kept returning 200s with correct completions; the only symptoms were the cache miss rate and the bill.

The cause: PR #31364 moved every role: "system" entry in messages into the top-level system field on the Invoke path, which invalidates every cache breakpoint past the tool definitions and system prompt. The fix shipped July 10 in v1.91.2 (#32578, #32831, #32882), with regression tests that fail on pre-fix code.

We own this outcome entirely. The trigger was a poorly documented change in how new Claude models and Claude Code use system messages, but customers run a gateway precisely so they do not have to track provider quirks. Translating requests faithfully, including their caching semantics, is our core job and here we fell short. This post explains exactly what happened, why our testing and review failed to catch it, and what we have changed so this class of regression does not ship again.