When I loaded 18w01a, it crashed.
Here is the crash report:
---- Minecraft Crash Report ----
// Daisy, daisy...

Time: 1/6/18 12:13 PM
Description: Initializing game

com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Invalid escape sequence at line 4 column 38 path $.pack.description
at com.google.gson.internal.Streams.parse(Streams.java:60)
at com.google.gson.JsonParser.parse(JsonParser.java:84)
at com.google.gson.JsonParser.parse(JsonParser.java:59)
at sf.a(SourceFile:73)
at sf.a(SourceFile:66)
at sx.a(SourceFile:35)
at ss.a(SourceFile:38)
at su.a(SourceFile:33)
at bny.a(SourceFile:1170)
at bnv.an(SourceFile:439)
at bnv.a(SourceFile:367)
at net.minecraft.client.main.Main.main(SourceFile:140)
Caused by: com.google.gson.stream.MalformedJsonException: Invalid escape sequence at line 4 column 38 path $.pack.description
at com.google.gson.stream.JsonReader.syntaxError(JsonReader.java:1559)
at com.google.gson.stream.JsonReader.readEscapeCharacter(JsonReader.java:1550)
at com.google.gson.stream.JsonReader.nextQuotedValue(JsonReader.java:1004)
at com.google.gson.stream.JsonReader.nextString(JsonReader.java:815)
at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:718)
at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:739)
at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:739)
at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:714)
at com.google.gson.internal.Streams.parse(Streams.java:48)
... 11 more

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Thread: Client thread
Stacktrace:
at com.google.gson.internal.Streams.parse(Streams.java:60)
at com.google.gson.JsonParser.parse(JsonParser.java:84)
at com.google.gson.JsonParser.parse(JsonParser.java:59)
at sf.a(SourceFile:73)
at sf.a(SourceFile:66)
at sx.a(SourceFile:35)
at ss.a(SourceFile:38)
at su.a(SourceFile:33)
at bny.a(SourceFile:1170)
at bnv.an(SourceFile:439)

– Initialization –
Details:
Stacktrace:
at bnv.a(SourceFile:367)
at net.minecraft.client.main.Main.main(SourceFile:140)

– System Details –
Details:
Minecraft Version: 18w01a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 192438528 bytes (183 MB) / 268435456 bytes (256 MB) up to 1073741824 bytes (1024 MB)
JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 18w01a
LWJGL: 3.1.2 build 29
OpenGL: ATI Radeon HD 2400 PRO GL version 2.1.8787, ATI Technologies Inc.
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because ARB_framebuffer_object is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: Yes
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs:
Current Language: ~_ERROR~ NullPointerException: null
Profiler Position: N/A (disabled)
CPU: 4x Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz