{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/system-1-x-learning-to-balance-fast-and-slow","title":"System-1.x: Learning to Balance Fast and Slow Planning with Language Models","arxiv_id":"2407.14414","date":"2024-07-19","proceeding":null,"authors":["Swarnadeep Saha","Archiki Prasad","Justin Chih-Yao Chen","Peter Hase","Elias Stengel-Eskin","Mohit Bansal"],"abstract":"Language models can be used to solve long-horizon planning problems in two distinct modes: a fast 'System-1' mode, directly generating plans without any explicit search or backtracking, and a slow 'System-2' mode, planning step-by-step by explicitly searching over possible actions. While System-2 is typically more effective, it is also more computationally expensive, making it infeasible for long plans or large action spaces. Moreover, isolated System-1 or 2 ignores the user's end goals, failing to provide ways to control the model's behavior. To this end, we propose the System-1.x Planner, a controllable planning framework with LLMs that is capable of generating hybrid plans and balancing between the two planning modes based on the difficulty of the problem at hand. System-1.x consists of (i) a controller, (ii) a System-1 Planner, and (iii) a System-2 Planner. Based on a user-specified hybridization factor (x) governing the mixture between System-1 and 2, the controller decomposes a problem into sub-goals, and classifies them as easy or hard to be solved by either System-1 or 2, respectively. We fine-tune all three components on top of a single base LLM, requiring only search traces as supervision. Experiments with two diverse planning tasks -- Maze Navigation and Blocksworld -- show that our System-1.x Planner outperforms a System-1 Planner, a System-2 Planner trained to approximate A* search, and also a symbolic planner (A*). We demonstrate the following key properties of our planner: (1) controllability: increasing the hybridization factor (e.g., System-1.75 vs 1.5) performs more search, improving performance, (2) flexibility: by building a neuro-symbolic variant with a neural System-1 and a symbolic System-2, we can use existing symbolic methods, and (3) generalizability: by being able to learn from different search algorithms, our method is robust to the choice of search algorithm.","url_abs":"https://arxiv.org/abs/2407.14414v2","url_pdf":"https://arxiv.org/pdf/2407.14414v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"abstracts"},"code_links":[{"paper_slug":"system-1-x-learning-to-balance-fast-and-slow","repo_url":"https://github.com/swarnaHub/System-1.x","is_official":1,"mentioned_in_paper":0,"mentioned_in_github":1,"framework":"pytorch","reach":null}],"tasks":[],"methods":[{"method_slug":"base","method_name":"BASE"}],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":"https://syntology.ai/paper/2407.14414","atlas_url":"https://app.syntology.ai/?focus=2407.14414","mcp":{"get_harvested_code_for_paper":{"arxiv_id":"2407.14414"}},"developers":"https://syntology.ai/developers","read_at":"2026-09-25T09:33:49+00:00","read_at_is":"when the build read Syntology's graph, not when any sample ran","claim":"Per-sample execution status on synthesized fixtures; not a correctness claim about the paper. Samples come from repositories linked to the paper, official or community; repo_kind says which.","repos":[{"provenance":"external:paperswithcode_snapshot_2025-07-28","url":"https://github.com/swarnaHub/System-1.x","reach":null}],"summary":{"ran_fixture":1,"ran_draft_wrong":3},"by_repo_kind":{"official":{"samples":4,"ran":4,"repositories":1}},"repo_kind_vocabulary":{"official":"The archive marks this repository official for the paper","named_in_paper":"The archive records that the paper mentions this repository; it is not marked official","listed":"In the archive's code links for this paper, not marked official and not recorded as mentioned in the paper","found_in_text":"Syntology found this repository in the paper's own text; whether it is the authors' implementation is not asserted","community":"Not in the archive's code links for this paper; a community repository Syntology harvested"},"n_pointer_only_for_licence":0,"samples":[{"code_sha256_prefix":"727641ce5801688d","entry":"convert_decomp_to_subgoals","repo":"swarnahub/system-1.x","repo_kind":"official","path":"src_blocksworld/decomp_hybrid.py","file_url":"https://github.com/swarnahub/system-1.x/blob/HEAD/src_blocksworld/decomp_hybrid.py","link_basis":"first_harvest_node","language":"python","status":"ran_fixture","verification_level":1,"contract_check":"RAISES","metamorphic_tier":"deterministic","behaviour_fingerprint":false,"licence":"MIT","inline_ok":true,"mcp_get_code":{"code_sha256":"727641ce5801688d"}},{"code_sha256_prefix":"afd0361425c8317a","entry":"generate_interleaved_meta_plan","repo":"swarnaHub/System-1.x","repo_kind":"official","path":"src_blocksworld/decomp_hybrid.py","file_url":"https://github.com/swarnaHub/System-1.x/blob/HEAD/src_blocksworld/decomp_hybrid.py","link_basis":"first_harvest_node","language":"python","status":"ran_draft_wrong","verification_level":1,"contract_check":"OUTPUT_MISDECLARED","metamorphic_tier":"deterministic","behaviour_fingerprint":false,"licence":"MIT","inline_ok":true,"mcp_get_code":{"code_sha256":"afd0361425c8317a"}},{"code_sha256_prefix":"5916a61d02ecd5c2","entry":"get_planner_prompt","repo":"swarnahub/system-1.x","repo_kind":"official","path":"src_blocksworld/decomp_hybrid.py","file_url":"https://github.com/swarnahub/system-1.x/blob/HEAD/src_blocksworld/decomp_hybrid.py","link_basis":"first_harvest_node","language":"python","status":"ran_draft_wrong","verification_level":1,"contract_check":"OUTPUT_MISDECLARED","metamorphic_tier":"deterministic","behaviour_fingerprint":false,"licence":"MIT","inline_ok":true,"mcp_get_code":{"code_sha256":"5916a61d02ecd5c2"}},{"code_sha256_prefix":"60f5d4368313ca9c","entry":"verbalize_state","repo":"swarnaHub/System-1.x","repo_kind":"official","path":"src_blocksworld/decomp_hybrid.py","file_url":"https://github.com/swarnaHub/System-1.x/blob/HEAD/src_blocksworld/decomp_hybrid.py","link_basis":"first_harvest_node","language":"python","status":"ran_draft_wrong","verification_level":1,"contract_check":"OUTPUT_MISDECLARED","metamorphic_tier":null,"behaviour_fingerprint":false,"licence":"MIT","inline_ok":true,"mcp_get_code":{"code_sha256":"60f5d4368313ca9c"}}]},"arxiv_metadata":null,"syntology_extracted_results":null}