diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,17 @@
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
-## 0.3.1.0 - 2020-04-21
+## 0.4.0.0 - 2021-06-22
+
+### Changed
+
+ - `OutputInfo.path` is optional
+
+### Added
+
+ - `ResultTypeBuildLogLine`
+
+## 0.3.1.0 - 2021-04-21
 
 ### Added
 
diff --git a/hercules-ci-api-agent.cabal b/hercules-ci-api-agent.cabal
--- a/hercules-ci-api-agent.cabal
+++ b/hercules-ci-api-agent.cabal
@@ -1,7 +1,7 @@
 cabal-version: 1.12
 
 name:           hercules-ci-api-agent
-version:        0.3.1.0
+version:        0.4.0.0
 synopsis:       API definition for Hercules CI Agent to talk to hercules-ci.com or Hercules CI Enterprise
 category:       API, CI, Testing, DevOps, Nix
 homepage:       https://github.com/hercules-ci/hercules-ci-agent#readme
diff --git a/src/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfo.hs b/src/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfo.hs
--- a/src/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfo.hs
+++ b/src/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfo.hs
@@ -32,7 +32,7 @@
       fixup = _Object . at "requiredSystemFeatures" %~ (<|> Just (A.Array mempty))
 
 data OutputInfo = OutputInfo
-  { path :: Text,
+  { path :: Maybe Text,
     isFixed :: Bool
   }
   deriving (Generic, Show, Eq, NFData, ToJSON, FromJSON)
diff --git a/src/Hercules/API/Logs/LogEntry.hs b/src/Hercules/API/Logs/LogEntry.hs
--- a/src/Hercules/API/Logs/LogEntry.hs
+++ b/src/Hercules/API/Logs/LogEntry.hs
@@ -23,6 +23,9 @@
 pattern ResultTypeProgress :: ResultType
 pattern ResultTypeProgress = ResultType 105
 
+pattern ResultTypeBuildLogLine :: ResultType
+pattern ResultTypeBuildLogLine = ResultType 101
+
 data Field = Int !Word64 | String !Text
   deriving (Eq, Show, Generic, NFData)
 
diff --git a/test/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfoSpec.hs b/test/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfoSpec.hs
--- a/test/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfoSpec.hs
+++ b/test/Hercules/API/Agent/Evaluate/EvaluateEvent/DerivationInfoSpec.hs
@@ -10,11 +10,11 @@
 objectV1, objectV2 :: DerivationInfo
 jsonV1, jsonV2 :: BL.ByteString
 jsonV1 = "{\"inputDerivations\":{\"/nix/store/1kircip4wskspsqqzxbmh6ss73iqh9ah-bash-4.4-p23.drv\":[\"out\"],\"/nix/store/0si75icim8ajxcsp25d9c52m42kqg1xj-stdenv-linux.drv\":[\"out\"],\"/nix/store/5kpp7mly0qad7l451xhr60k0wbv6vivi-jquery-1.11.3.drv\":[\"out\"],\"/nix/store/kyxayhm3r6gpzbg1d57fwb8m7gkmpwcy-nixos-test-driver-agent-test.drv\":[\"out\"],\"/nix/store/qzvim3ca1s5zxbbvpzzipizfnfpdf5r2-libxslt-1.1.33.drv\":[\"dev\"],\"/nix/store/id49f28qvggmzpmlxp511v6yhc070lkf-jquery-ui-1.11.4.drv\":[\"out\"]},\"platform\":\"x86_64-linux\",\"inputSources\":[\"/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh\",\"/nix/store/fs6a6m9s5n367dslsvsl9lg89h3ns3ya-logfile.css\",\"/nix/store/jjh6h82n5rhw45badlpbj1yv7y6m48h2-log2html.xsl\",\"/nix/store/kdangwwh47ngwxk859ibbvkj4vmm9rzr-treebits.js\"],\"outputs\":{\"out\":{\"path\":\"/nix/store/7vg7ij5933dhg6dh22fvs90bbzmzg8kj-vm-test-run-agent-test\",\"isFixed\":false}},\"derivationPath\":\"testdata/vm-test-run-agent-test.drv\"}"
-objectV1 = DerivationInfo {derivationPath = "testdata/vm-test-run-agent-test.drv", platform = "x86_64-linux", requiredSystemFeatures = [], inputDerivations = fromList [("/nix/store/0si75icim8ajxcsp25d9c52m42kqg1xj-stdenv-linux.drv", ["out"]), ("/nix/store/1kircip4wskspsqqzxbmh6ss73iqh9ah-bash-4.4-p23.drv", ["out"]), ("/nix/store/5kpp7mly0qad7l451xhr60k0wbv6vivi-jquery-1.11.3.drv", ["out"]), ("/nix/store/id49f28qvggmzpmlxp511v6yhc070lkf-jquery-ui-1.11.4.drv", ["out"]), ("/nix/store/kyxayhm3r6gpzbg1d57fwb8m7gkmpwcy-nixos-test-driver-agent-test.drv", ["out"]), ("/nix/store/qzvim3ca1s5zxbbvpzzipizfnfpdf5r2-libxslt-1.1.33.drv", ["dev"])], inputSources = ["/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh", "/nix/store/fs6a6m9s5n367dslsvsl9lg89h3ns3ya-logfile.css", "/nix/store/jjh6h82n5rhw45badlpbj1yv7y6m48h2-log2html.xsl", "/nix/store/kdangwwh47ngwxk859ibbvkj4vmm9rzr-treebits.js"], outputs = fromList [("out", OutputInfo {path = "/nix/store/7vg7ij5933dhg6dh22fvs90bbzmzg8kj-vm-test-run-agent-test", isFixed = False})]}
+objectV1 = DerivationInfo {derivationPath = "testdata/vm-test-run-agent-test.drv", platform = "x86_64-linux", requiredSystemFeatures = [], inputDerivations = fromList [("/nix/store/0si75icim8ajxcsp25d9c52m42kqg1xj-stdenv-linux.drv", ["out"]), ("/nix/store/1kircip4wskspsqqzxbmh6ss73iqh9ah-bash-4.4-p23.drv", ["out"]), ("/nix/store/5kpp7mly0qad7l451xhr60k0wbv6vivi-jquery-1.11.3.drv", ["out"]), ("/nix/store/id49f28qvggmzpmlxp511v6yhc070lkf-jquery-ui-1.11.4.drv", ["out"]), ("/nix/store/kyxayhm3r6gpzbg1d57fwb8m7gkmpwcy-nixos-test-driver-agent-test.drv", ["out"]), ("/nix/store/qzvim3ca1s5zxbbvpzzipizfnfpdf5r2-libxslt-1.1.33.drv", ["dev"])], inputSources = ["/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh", "/nix/store/fs6a6m9s5n367dslsvsl9lg89h3ns3ya-logfile.css", "/nix/store/jjh6h82n5rhw45badlpbj1yv7y6m48h2-log2html.xsl", "/nix/store/kdangwwh47ngwxk859ibbvkj4vmm9rzr-treebits.js"], outputs = fromList [("out", OutputInfo {path = Just "/nix/store/7vg7ij5933dhg6dh22fvs90bbzmzg8kj-vm-test-run-agent-test", isFixed = False})]}
 
 jsonV2 = "{\"inputDerivations\":{\"/nix/store/1kircip4wskspsqqzxbmh6ss73iqh9ah-bash-4.4-p23.drv\":[\"out\"],\"/nix/store/0si75icim8ajxcsp25d9c52m42kqg1xj-stdenv-linux.drv\":[\"out\"],\"/nix/store/5kpp7mly0qad7l451xhr60k0wbv6vivi-jquery-1.11.3.drv\":[\"out\"],\"/nix/store/kyxayhm3r6gpzbg1d57fwb8m7gkmpwcy-nixos-test-driver-agent-test.drv\":[\"out\"],\"/nix/store/qzvim3ca1s5zxbbvpzzipizfnfpdf5r2-libxslt-1.1.33.drv\":[\"dev\"],\"/nix/store/id49f28qvggmzpmlxp511v6yhc070lkf-jquery-ui-1.11.4.drv\":[\"out\"]},\"platform\":\"x86_64-linux\",\"inputSources\":[\"/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh\",\"/nix/store/fs6a6m9s5n367dslsvsl9lg89h3ns3ya-logfile.css\",\"/nix/store/jjh6h82n5rhw45badlpbj1yv7y6m48h2-log2html.xsl\",\"/nix/store/kdangwwh47ngwxk859ibbvkj4vmm9rzr-treebits.js\"],\"outputs\":{\"out\":{\"path\":\"/nix/store/7vg7ij5933dhg6dh22fvs90bbzmzg8kj-vm-test-run-agent-test\",\"isFixed\":false}},\"derivationPath\":\"testdata/vm-test-run-agent-test.drv\",\"requiredSystemFeatures\":[\"kvm\",\"nixos-test\"]}"
 
-objectV2 = DerivationInfo {derivationPath = "testdata/vm-test-run-agent-test.drv", platform = "x86_64-linux", requiredSystemFeatures = ["kvm", "nixos-test"], inputDerivations = fromList [("/nix/store/0si75icim8ajxcsp25d9c52m42kqg1xj-stdenv-linux.drv", ["out"]), ("/nix/store/1kircip4wskspsqqzxbmh6ss73iqh9ah-bash-4.4-p23.drv", ["out"]), ("/nix/store/5kpp7mly0qad7l451xhr60k0wbv6vivi-jquery-1.11.3.drv", ["out"]), ("/nix/store/id49f28qvggmzpmlxp511v6yhc070lkf-jquery-ui-1.11.4.drv", ["out"]), ("/nix/store/kyxayhm3r6gpzbg1d57fwb8m7gkmpwcy-nixos-test-driver-agent-test.drv", ["out"]), ("/nix/store/qzvim3ca1s5zxbbvpzzipizfnfpdf5r2-libxslt-1.1.33.drv", ["dev"])], inputSources = ["/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh", "/nix/store/fs6a6m9s5n367dslsvsl9lg89h3ns3ya-logfile.css", "/nix/store/jjh6h82n5rhw45badlpbj1yv7y6m48h2-log2html.xsl", "/nix/store/kdangwwh47ngwxk859ibbvkj4vmm9rzr-treebits.js"], outputs = fromList [("out", OutputInfo {path = "/nix/store/7vg7ij5933dhg6dh22fvs90bbzmzg8kj-vm-test-run-agent-test", isFixed = False})]}
+objectV2 = DerivationInfo {derivationPath = "testdata/vm-test-run-agent-test.drv", platform = "x86_64-linux", requiredSystemFeatures = ["kvm", "nixos-test"], inputDerivations = fromList [("/nix/store/0si75icim8ajxcsp25d9c52m42kqg1xj-stdenv-linux.drv", ["out"]), ("/nix/store/1kircip4wskspsqqzxbmh6ss73iqh9ah-bash-4.4-p23.drv", ["out"]), ("/nix/store/5kpp7mly0qad7l451xhr60k0wbv6vivi-jquery-1.11.3.drv", ["out"]), ("/nix/store/id49f28qvggmzpmlxp511v6yhc070lkf-jquery-ui-1.11.4.drv", ["out"]), ("/nix/store/kyxayhm3r6gpzbg1d57fwb8m7gkmpwcy-nixos-test-driver-agent-test.drv", ["out"]), ("/nix/store/qzvim3ca1s5zxbbvpzzipizfnfpdf5r2-libxslt-1.1.33.drv", ["dev"])], inputSources = ["/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh", "/nix/store/fs6a6m9s5n367dslsvsl9lg89h3ns3ya-logfile.css", "/nix/store/jjh6h82n5rhw45badlpbj1yv7y6m48h2-log2html.xsl", "/nix/store/kdangwwh47ngwxk859ibbvkj4vmm9rzr-treebits.js"], outputs = fromList [("out", OutputInfo {path = Just "/nix/store/7vg7ij5933dhg6dh22fvs90bbzmzg8kj-vm-test-run-agent-test", isFixed = False})]}
 
 spec :: Spec
 spec = do