1 00:00:00,100 --> 00:00:02,940 You know, if there is one thing that gets my motor running in the shed, 2 00:00:03,340 --> 00:00:07,200 it is making developer workflows fly without burning a hole in your pocket. 3 00:00:08,160 --> 00:00:13,020 Before we dive in, quick shoutout to our sponsor Jellypod AI for making this episode 4 00:00:13,120 --> 00:00:13,500 possible. 5 00:00:13,992 --> 00:00:15,172 Yeah, absolutely! 6 00:00:15,532 --> 00:00:20,532 And today we have to talk about a massive fix that landed in Claude Code version 7 00:00:20,892 --> 00:00:23,452 2.1.275. 8 00:00:24,212 --> 00:00:27,872 If you have been using custom system prompts with the system prompt flag, 9 00:00:28,352 --> 00:00:30,372 you might have been unknowingly burning money. 10 00:00:30,638 --> 00:00:31,378 Wait, how so? 11 00:00:31,698 --> 00:00:33,878 Was it, uh, missing the cache entirely? 12 00:00:34,240 --> 00:00:34,700 Exactly. 13 00:00:35,300 --> 00:00:38,980 Developers were putting things like git commit SHAs, build timestamps, 14 00:00:39,060 --> 00:00:41,840 or environment variables right at the top of their prompt files. 15 00:00:42,360 --> 00:00:46,520 And because Anthropic's prompt cache relies on exact prefix matching from the top 16 00:00:46,600 --> 00:00:51,600 down, changing a single date string busted the entire prompt cache on every single 17 00:00:51,720 --> 00:00:51,980 turn. 18 00:00:52,420 --> 00:00:53,520 Oh, oof! 19 00:00:54,540 --> 00:00:59,420 That is like, er, busting the entire cache because a timestamp changed on a static 20 00:00:59,500 --> 00:00:59,800 image. 21 00:01:01,480 --> 00:01:03,200 It is basically like web caching, right? 22 00:01:03,940 --> 00:01:08,000 You want your big static library files sitting on a global CDN with a super long 23 00:01:08,100 --> 00:01:12,200 time to live, while your dynamic user session stuff gets calculated on the fly. 24 00:01:12,430 --> 00:01:14,590 That is the perfect analogy. 25 00:01:15,130 --> 00:01:19,790 And to solve this, Anthropic added a special sentinel line: double underscore SYSTEM 26 00:01:19,890 --> 00:01:22,430 PROMPT DYNAMIC BOUNDARY double underscore. 27 00:01:22,500 --> 00:01:23,220 Right, right. 28 00:01:23,247 --> 00:01:27,540 So everything above that magic boundary line gets treated as a static array prefix 29 00:01:27,620 --> 00:01:29,940 and cached globally across requests. 30 00:01:29,958 --> 00:01:30,598 Yes! 31 00:01:30,678 --> 00:01:35,558 And anything below that line is treated as dynamic context per request. 32 00:01:35,771 --> 00:01:41,158 In long running sessions, this cuts input token costs by up to 90 percent. 33 00:01:41,267 --> 00:01:42,267 Ninety percent! 34 00:01:42,887 --> 00:01:44,727 Crikey, that is serious savings. 35 00:01:44,792 --> 00:01:45,712 It really is. 36 00:01:45,737 --> 00:01:49,992 Picture a CI CD code review workflow where you run claude with a custom system 37 00:01:50,026 --> 00:01:54,152 prompt file like dot claude slash review prompt dot txt. 38 00:01:54,299 --> 00:01:57,832 Above the boundary line, you put your org wide linting rules, 39 00:01:57,876 --> 00:02:00,632 security guidelines, and architectural standards. 40 00:02:00,760 --> 00:02:04,872 Then below the boundary line, you put the PR author's name and the commit time. 41 00:02:05,095 --> 00:02:06,055 Ah, gotcha. 42 00:02:07,135 --> 00:02:10,935 So all those heavy company rules stay cached for every build, 43 00:02:11,415 --> 00:02:13,595 and only the PR metadata shifts. 44 00:02:13,908 --> 00:02:14,608 Exactly. 45 00:02:15,008 --> 00:02:20,148 But there is a huge caveat developers need to watch out for: byte matching above 46 00:02:20,208 --> 00:02:22,468 that boundary line is strictly enforced. 47 00:02:23,008 --> 00:02:28,548 If your text editor changes line endings from LF to CR LF, or adds a sneaky space at 48 00:02:28,588 --> 00:02:31,828 the end of a line above the boundary, boom, full cache miss. 49 00:02:32,635 --> 00:02:34,695 Classic invisible whitespace trap! 50 00:02:35,055 --> 00:02:37,655 That will get you every time if you are not careful. 51 00:02:38,555 --> 00:02:38,995 Oh yeah. 52 00:02:39,695 --> 00:02:45,615 But speaking of sneaky invisible stuff, version 2.1.277 brought another great 53 00:02:45,675 --> 00:02:48,995 quality of life fix: automatic prompt sanitization. 54 00:02:49,510 --> 00:02:50,950 What kind of sanitization? 55 00:02:51,042 --> 00:02:55,842 It automatically strips invisible Unicode formatting tags and zero width spaces from 56 00:02:55,902 --> 00:02:57,522 prompts before sending them. 57 00:02:57,629 --> 00:03:02,162 Turns out attackers were hiding prompt injection payload instructions inside zero 58 00:03:02,215 --> 00:03:03,922 width Unicode characters! 59 00:03:04,638 --> 00:03:05,318 No way! 60 00:03:05,598 --> 00:03:07,018 Invisible prompt injection? 61 00:03:07,598 --> 00:03:09,778 That is sneaky as a snake in the grass. 62 00:03:09,917 --> 00:03:10,157 Right? 63 00:03:10,177 --> 00:03:14,317 Now Claude Code cleans them out and shows you the clean text before executing. 64 00:03:14,333 --> 00:03:14,893 Love that. 65 00:03:15,133 --> 00:03:18,333 What else shipped recently in the terminal tool? 66 00:03:18,333 --> 00:03:24,733 Well, in 2.1.275, if you run claude plugin install with a marketplace flag pointing 67 00:03:24,786 --> 00:03:29,613 to an unregistered source, it detects it and asks if you want to auto register that 68 00:03:29,660 --> 00:03:31,133 marketplace in one command. 69 00:03:31,167 --> 00:03:33,807 Nice, no separate configuration step needed. 70 00:03:33,833 --> 00:03:39,993 And in 2.1.278, they added an Auto mode server status row when you run slash 71 00:03:40,073 --> 00:03:44,713 status, so you can immediately see if your session's auto mode classifier is running 72 00:03:44,770 --> 00:03:48,633 server side where it does not charge you extra classifier token overhead. 73 00:03:48,807 --> 00:03:52,867 Clean cost savings, better security, and smoother plugin installs. 74 00:03:53,527 --> 00:03:55,787 Gotta love when point releases pack this much punch. 75 00:03:56,387 --> 00:03:57,447 Good chatting as always!