Source:
The RegisterDevelopers report model thinking blocks being returned empty or truncated
Anthropic's ClaudeCode appears to be having trouble displaying summaries of its "thinking," according to several bug reports, while the underlying
reasoningtokens still cost money. According to complaints, the API has been returning empty thinking blocks for Opus 4.8 and Sonnet 5 even when users explicitly request summarized thinking. Models from several sources can display their "thinking," a process that gives models additional tokens to reason through complex problems before producing a response. Software with this capability delivers a summary that explains how it tackled a task. Some can also indulge in "extended thinking," though this capability is now deprecated. Developers often enable "thinking" in the hope that it produces better results, at the cost of additional tokens and latency. Developer Michael Hood has noticed that some of Anthropic's models are currently not always good at sharing their thinking. "As of 2026-07-16 ~15:00Z, the API returns empty thinking blocks (thinking: '', signature only) for Claude Opus 4.8 and Sonnet 5, even when display: 'summarized' is explicitly requested — including when injected directly into the raw request body," Hood recently observed. We're told this issue is under investigation but doesn't appear to be a broad, ongoing concern. It may simply be an artefact of tests that change how Anthripic displays summaries. Similar behavior involving missing thinking blocks has been reported in Claude Code for VS Code. Another bug report claims thinking block summaries are being truncated while
tokenbills are not adjusted accordingly. "The thinking is generated (and billed) in full; a portion of the summary stream is silently dropped," the anonymous author claims. This particular claim, that customers are being billed for text not delivered, may follow from a misunderstanding of Anthropic's terms: "You are charged for all thinking tokens generated, even when collapsed or redacted," the company's documentation explains. Under that legalese, a thinking summary costs the same as the full output. And it's unclear whether bug-based truncation would change the billing picture. "Thinking has a cost: the tokens Claude spends reasoning are billed as output tokens, even when the thinking text isn't returned to you, and they count toward max_tokens alongside the response text," the company explains. To reduce spending on thinking, customers are advised to lower their budget setting or disable thinking. Separately, the Anthropic API has been seen terminating data streams during long-running thinking sessions. There have been at least seven other related API bug reports, but the streaming issue identified by developer Hector Bernstorff describes client-side defects. The Register understands this particular issue has to do with tuning network behavior, specifically to terminate or retry long running requests. Work is ongoing to balance perceived latency against the risk of requests getting stuck. "Claude Code ships updates nearly every day, and reports from the community like these GitHub issues are a big part of how we catch problems quickly," an Anthropic spokesperson told The Register. "We're grateful to the developers who take the time to file them, and we'll keep fixing things as they come up." ®
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Key Terms Explained #
Anthropic
An AI safety company founded in 2021 by former OpenAI researchers, including Dario and Daniela Amodei.
Claude
Anthropic's family of AI assistants, including Claude Haiku, Sonnet, and Opus.
Reasoning
The ability of AI models to draw conclusions, solve problems logically, and work through multi-step challenges.
Token
The basic unit of text that language models work with.