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Anthropic’s Lance Martin: old prompting habits raise the cost of new Claude models
Frontier models no longer need instructions such as ‘think step by step’, which instead add costs and can weaken results, said Anthropic’s Lance Martin. A skill in Claude Code finds and removes them from prompts.
Lance Martin, a member of technical staff at Anthropic, called for stripping out prompt habits that helped earlier models in a talk published on the AI Engineer channel on 6 November 2026. Prompts accumulate technical debt just as code does, Martin said.
Martin’s examples included the instruction ‘think step by step’, requests to check work such as ‘double-check your work’, emphasis such as ‘be maximally thorough’ and scratchpads supplied to the model in advance. Frontier models decide for themselves when to think and check their work anyway, Martin said. Extra instructions add costs and can weaken results.
Contradictory rules also do more harm now, Martin said. Earlier models followed instructions more loosely and ignored one of the conflicting rules, so the prompt still worked. Frontier models, by contrast, often get confused by the contradiction.
Martin’s own test
Martin built a synthetic test of about 50 customer support tickets. Martin simulated a move from Opus 4.8 to Opus 5.5 and added each harmful habit to the prompts separately. Switching models alone cut costs and slightly improved results. After the prompt audit, results improved and costs fell further. Martin gives no exact figures in the talk, and the chart in the presentation could not be verified. The model names are based on YouTube’s automatic captions.
Martin cannot say exactly from which model onwards the old habits are no longer needed, but estimates the cut-off at roughly Opus 4.5. The skill also includes model-specific guidance. Martin said Haiku, for example, may need more emphasis, but was unsure whether this holds.
Cache and reasoning effort
The prompt cache processes a prompt prefix that repeats across turns more quickly and cheaply. Martin put its cost at about a tenth of the base price. The price varies by model. The cache works only if the prefix is exactly the same; changing a single byte invalidates it. Martin advises placing the system instructions and tools shared by all sessions first, followed by the CLAUDE.md file, session state and messages.
Martin and colleagues ran Claude Code’s cache check on Anthropic’s internal benchmarks. They found that costs could be cut by up to 72 per cent without a meaningful change in performance. Some of the benchmark harnesses were not using the cache correctly. A harness is the program that controls an agent: it gives the model its tools and runs its steps.
Martin recommends starting with a stronger model, such as Opus 5.5, at low reasoning effort. This often uses fewer tokens than a weaker model at high effort, Martin said. In the same support ticket test, an automated improvement loop (hill climbing) changed the model, reasoning effort and prompt. Costs fell by 90 per cent and results improved. The loop is not flawless, Martin said, and its results must be checked carefully.
The prompt audit is a skill included in Claude Code. Users can launch it through the checkup skill or the Claude API skill. The skill removes harmful habits from the skills, tools and prompts in the working directory. Because it edits files, it is worth reviewing the changes, for example in version control, before adopting them.