{"schema_version":"onlylabs.public_signal.v1","title":"Anthropic Writing: Harness Design Long Running Apps","description":"Anthropic writing signal with public source context, captured evidence pages, related signals, and data-business radar classification.","url":"https://onlylabs.fyi/signals/081d3569-243e-4e71-9809-9ec54248ddbf","json_url":"https://onlylabs.fyi/signals/081d3569-243e-4e71-9809-9ec54248ddbf/signal.json","generated_at":"2026-06-11T03:06:11.214804+00:00","org":{"slug":"anthropic","name":"Anthropic","category":"frontier-lab","category_label":"Frontier lab","dossier_url":"https://onlylabs.fyi/labs/anthropic","dossier_json_url":"https://onlylabs.fyi/labs/anthropic/dossier.json"},"related_urls":{"signal":"https://onlylabs.fyi/signals/081d3569-243e-4e71-9809-9ec54248ddbf","signal_json":"https://onlylabs.fyi/signals/081d3569-243e-4e71-9809-9ec54248ddbf/signal.json","source":"https://www.anthropic.com/engineering/harness-design-long-running-apps","lab_dossier":"https://onlylabs.fyi/labs/anthropic","lab_dossier_json":"https://onlylabs.fyi/labs/anthropic/dossier.json","analysis":"https://onlylabs.fyi/analysis/anthropic","analysis_json":"https://onlylabs.fyi/analysis/anthropic/analysis.json","analysis_evidence_json":"https://onlylabs.fyi/analysis/anthropic/evidence.json","category":"https://onlylabs.fyi/frontier","category_json":"https://onlylabs.fyi/frontier.json","category_feed":"https://onlylabs.fyi/frontier/feed.xml","category_signals_json":"https://onlylabs.fyi/signals.json","topic":"https://onlylabs.fyi/topics/talking","topic_signals_json":"https://onlylabs.fyi/topics/talking/signals.json","topic_feed":"https://onlylabs.fyi/topics/talking/feed.xml","data_business":null},"answer_pack":{"answer":"Anthropic published Harness Design Long Running Apps. 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narrative layer over raw signals and helps identify which frontier-lab priorities are becoming externally legible.","required_sources":[{"label":"signal_json","url":"https://onlylabs.fyi/signals/081d3569-243e-4e71-9809-9ec54248ddbf/signal.json","required":true},{"label":"source","url":"https://www.anthropic.com/engineering/harness-design-long-running-apps","required":true},{"label":"dossier_json","url":"https://onlylabs.fyi/labs/anthropic/dossier.json","required":true},{"label":"analysis_evidence_json","url":"https://onlylabs.fyi/analysis/anthropic/evidence.json","required":true},{"label":"topic_signals_json","url":"https://onlylabs.fyi/topics/talking/signals.json","required":false},{"label":"data_radar_json","url":null,"required":false}],"expected_output":["one-paragraph source-grounded interpretation","category-specific implication","confidence and missing evidence","recommended next source to inspect"],"prompt_seed":"Using only the linked onlylabs JSON, captured source context, and 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Taking inspiration from Generative Adversarial Networks (GANs), I designed a multi-agent structure with..."},"evidence_pages":[{"url":"https://www.anthropic.com/engineering/harness-design-long-running-apps","final_url":"https://www.anthropic.com/engineering/harness-design-long-running-apps","title":"Harness Design Long Running Apps","http_status":200,"content_type":"text/html; charset=utf-8","capture_method":"plain","fetched_at":"2026-06-11T03:06:11.214804+00:00","bytes":244324,"raw_path":"9fa759b72385cdecdf59660d48a3a9bd4f6f419e8a77026091818c594be75130.html","content_hash":"cd7cc2bca7899ba962128a012cdd37e9ca13909076ec1227b2308e1465fe388b","excerpt_chars":1200,"truncated":true,"excerpt":"Harness design for long-running application development \\ Anthropic Engineering at Anthropic Harness design for long-running application development Published Mar 24, 2026 Harness design is key to performance at the frontier of agentic coding. Here's how we pushed Claude further in frontend design and long-running autonomous software engineering. Written by Prithvi Rajasekaran, a member of our Labs team. Over the past several months I’ve been working on two interconnected problems: getting Claude to produce high-quality frontend designs, and getting it to build complete applications without human intervention. This work originated with earlier efforts on our frontend design skill and long-running coding agent harness , where my colleagues and I were able to improve Claude’s performance well above baseline through prompt engineering and harness design—but both eventually hit ceilings. To break through, I sought out novel AI engineering approaches that held across two quite different domains, one defined by subjective taste, the other by verifiable correctness and usability. 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